This study involves two protocols: 1) the extent to which frail, old men (n=80) can respond to 9 months of exercise training with the cardiovascular, musculoskeletal, and central nervous system adaptions that have been shown to occur in younger people and 2) if hormone replacement therapy (HRT) can reduce frailty in old women (n=120) with physical frailty, and to determine if 9 months of exercise training brings about greater improvements in old women who have been on HRT for 9 months than in sex hormone deficient women.